Spark-plug.



C. H. DUFFY.

SPARK PLUG.

APPLICATION FlLED JAN. 6. 1913.

Patented July "1, 1916 IV] 7 YVE SS1? 5 cnentizsnoeuno'sr OBI-NORTH LAUREL, MARYLAND.

' SPARK-PLUG.

To all whom it may concern Be it knovi'n that I,

' ing at North Laurel, inv the countyof Howtendency to short circuit the ard and State of'lviaryland, have invented certain new and useful Improvements lll Spark-Plugs; and I do declare the following- Generally speikingand with reference to spark plugs of ordinary construction it is possible; -to short circu t the same n three jways. .Flliit, by nieans of a brid e of short circuiting,materialusuch; asLoil aden with carlmn; water and the l ke extending across t'he sparlcgap and connecting the two electrodes. Secondb', by means of'a coating of carbon deposited on the insulator within the" 'shell of the plug' so as to provide an eleCt-rical conductor from the central electrode to the metal shell of the plug, and thirdly, by reason of the passage ofthe secondary current over the. surface o-f the insulator outside of the shell of thejplug, the current passing over the. insulator from the outer portion of the central electrode to the shell of the plug. i

This invention has for its object to prerent the short circuiting of the plug in any f these mentioned manners so as to insure a proper jumping or arcing of the secondary curren; at the spark gap.

A further ob ect of the invention is to so construct theinsulutor and. the centrulelectrode as to relieve the insulator of any undue stress or. strain which would; tend to crack or disrupt the insulator.

The coefficient of expansion of metals varies considerably according totheir characters and according to the alloys thereof, and it might be said as a general proposition that there is no metal or alloy ofinetals suitable for use as spam plug electrodes whose co- Specification or etters Patent.

Client-.35 i Huen' 'Dorrr, a citizen of the United States, I'CSldellicient of expansion is the same as that of porcelain which isthe usual material of which spark plug'insulators are constructed. The vcrmsequence of. this is that when the Patented July 4, 1916. f A micanmmeii aim-rm 6, Isis; scri i'no. 740,502]

plugis. subjected to the heat generated in an internal combustion enginethe expansion and contraction of the central metal electrode differs from the expansion and contraction of its surrounding'insulat0r,-thus placing upon the insulator undue stresses and strains which frequently; result in cracking or disrupting the insulator. thus rendering the plug useless to further hold the high tension current employed.

This invention consists in the novel con struction and arrangement of tlieelectrodes of the plug and in so. forming the same that a strong capillary attraction is exerted at the spark gap of the plug to brca-k'a short 7 circuiting bridge of liquid the spark .gap.

The inventionfurther consists in the construction of the insulator and of itlie metalshell of'the plug so as to allow theiloweripor tion of the insulator tofreely expand and "contract, and which isso .oonstructed'as to place in the path of. the-secondary"current sullicient resistance to prevent t-he'passage of the secondary currentorer-the inclosed current. Y

The invention further consistsin so con- Iportion of theinsulator to sliortgcircuit the v l structing the lower inclosed'portion of'the insulator that one or more clean annular' rings will be maintained around the lower portion of the insulator between the central electrode and the metal shell oi the plng' thereby providing a break in any deposit of short circuiting material so asto prevent the passage of the secondary. current over the 7 lower inclosed portion of the insulator.

The invention further consists in the construction of the insulaton'and the central electrode which places in the-path of the secondary current sufiicient resistance so as to prevent the passage of current over the outer exposed portion of the insulator. to short circuit the currentbetween the outer portion of the electrodeand the metal shell of the plug.

The invention further consists in certain other novel details of construction and in combinations of parts, all of, which will be first fully described and afterward specifically pointed outin the appended claims.

'trating a still further modification of the electrodes.

Like numerals of reference indicate the same parts throughout the several figures in which: I

1 indicates the spark plug and '2 the metal shell, said shell comprising the lower body portion 3 and the upper gland 4, the .said two parts being threaded together at 5 in the manner as illustrated in' Fig.1.

. The lower body portion 3 of the shell is provided with a relatively large bore 0 which communicates with the lower relatively small bore-7, an inclined shoulder 8 being formed between the two bores 6 and? in the manner as illustrated in Fig. 1, the extreme lower-portion of the shell surroundi-ng-the bore 7 being threaded'at 9 for threaded connection with the" combustion chamber of an internal combustion engine.

10 indicates the lower electrode of. the plug I which is preferably secured to the lower threaded end 9 of the plug in any convenient manner, thebody portion 3 of the shell being provided above the enlarged chamber 6 with a shoulder 11 to receive the insulating core in the manner as shown in Fig. '1, while the gland 4 of the shell is provided with an inwardly extending annular portion 12 to engage the insulating core in the manner as shown in the drawing, the said gland 4} being provided with an opening 13 sufiiciently large to permit of the said' gland passing freely overthe outer portion of the insulating core.

1 1 indicates the insulating core of the plug which may beconstructed of any suitable heat resisting insulating r'naterial, the said insulating core.14 being'shaped in the manner as illustrated in Fig. l, the extreme upper portion being preferably swelled as illustrated at 15 the said insulating core being provided at substantially the center thereof with an enlargement 16 providing suitable shoulders 17 and 18 for engagement with the body portion and gland of the shell.

19 indicates the lower inclosed portion of the insulating core, said lower inclosed portion being provided with a plurality of annular chambers 20, said annular chambers being deep and relatively narrow. while a plurality of annular webs or flanges 21 are formed on the lower inclosed portion of the insulating core by reason of the annular chambers 20, the same being arranged'in the insulating core being also provided with a relatively large central bore '24, said relatively large bore's 23 and 24 communicating with the small central bore '22; thereby forming a shoulder. above and' below the said small central bore 22 in the manner as shown in the drawing.

25 indicates the upper threaded portion ofv the central electrode26, said central electrode '26 being provided with aswell 27 or with a small threaded nut,' said s'wellor threaded nut 27- being of a size to snugly [it the relatively large bore 23 in the lower inclosed portion of the insulating core and to engage the shoulder below' the small central bore 22 in the manner-asshown in Fig. 1, a suitable gasket or other packing means bei'ngemployed' to prevent leakage through the insulating-core in the usual manner.

28 indicates the upper portion of the cen tral electrode which, as shown in the drawing, is provided with a lower enlarged portion 29, said lower enlarged portion being of a size to snugly fit the relatively large bore 24 in the upper portion of the insulating core, the said enlarged portion-29 being internally threaded to receive the .threaded end 25 of the lower electrode 26,.that part of the upper portion '28 ofthe electrode bei g reduced as shown at 3.0 inorder to prevent contact with the wall of the relatively large bore 24- in the manner as shown in Fig. 1. An annular flange 31 is formed above the reduced portion 30. and is of such 'a'size as to cover the endofthe relatively large opening 24 but which is not in contact with the upper end of theinsulating Q core -an annular groove 32 being provided above the annular flange 31 to receivea wire terminal; the extreme upper end of the portion 28 being headed at 33' to provide a finish for this portion,' the secondary wire terminal being held between the head 33 and the annular-flange 31 in the manner which will be perfectly apparent from an inspection of the accompanying drawing.

The extreme lower end of the central electrode 26 is provided with a long and rela- 211: mp2! in? PM (re in: ventral Hm. t

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ran-J Ref Pribed it win he Liwji hie 1 V emvtrndei n P in the man 2 43- 'minQf either ZWJUU prm'mw Kinda i gamma-1 Ange! Km 35 open fz-mn (am 45 essvntml in M2! slut n1 m1 i am % "hunpm will become foul with a coating of short circuiting material but the extreme bottoms of the said deep annular chambers 20 are maintained in a relatively clean and uncoated condition. It therefore matters not how foul or coated the said surfaces of the insulator become so long as there is a single clean ring maintained around the lower portion of the insulator, for the reason that the current in order to short circuit over the surface of the insulator must have a continuous path and any break or series of breaks will ef' fectually prevent the passage of the current over the inclosed portion.of the insulator, and so long as the extreme bottoms of the said annular chambers 20 are maintained in a clean condition the coated portions of the insulator do not provide a conductor for the passage of the current over the same. This obviously would not exist to the same extent if the lower inclosed portion of the insulator extended down into the lower bore or chamber 7 as the deep. annular chambers 20 in the insulator would then be subjected to the foul gas of the combustion chamber and would more readily accuu'iulate a coating of short circuiting material which would doubtless extend to the bottoms of the said annular chambers 20. The arrangement of the annular chamber 6 surrounding the lower insulating core and the relatively small lower bore or chamber 7 prevents the foul gases from the combustion chamber from entering the bottoms of the annular chambers 20 in the insulating core while the fact that the extreme lower surface of the insulating core extends beyond the edges of the lower bore or chamber 7 causes the major portion of the foul gases to deposit their short circuiting material upon the extreme lower surface of the insulating core. Plugs constructed in accordance with this inven tion when subjected to extreme conditions of oil and carbon have shown conclusively that nearly the entire deposit of carbon has occurred on the extreme lower surface of the insulating core, while the extreme bottoms of the annular chamber 7 were maintained in a clean condition even after the constant use of the plug for a. period extending over six months. It will be further noted that the relatively large central bore 23 in the insulating core extends inwardly of the core a distance greater than the lower depending inclosed portion of the core. thus allowing the depending portion of the core to be free of all stresses and strains which might otherwise tend to crack or disrupt the insulator by reason of the external chambered construction thereof. It will therefore be understood from an inspection of Fig. 1 that the current to pass over the surface of the lower inclosed portion of the plug? must start at the extreme inner end of the rela tively large bore 23, pass downwardly along the walls thereof to the extreme lower end of the insulating core and then pass upwardly over the sides of the inclosed portion of the core following the contour of each of the annular chambers 20. That the current cannot pass in this direction if any one of the bottoms of the said annular chambers 20 is maintained in a clean condition is perfectly apparent from an inspection of the accompanying drawing taken in connection with the above description and explanation.

Referring now to the upper exposed portion of the insulator it will be seen that the upper portion 28 of the electrode passes a considerable distance within the relatively large bore 24, the lower enlarged portion 29 of the said electrode member being in contact with the insulator only at the lower portion of said member. When the two parts of the electrode are threaded together and preferably cemented in position no part of the upper portion of the electrode member 28 is in contact with the said insulator, and consequently current passing into the upper electrode member 28 does not come in contact with the outer exposed portion of the insulator but does come in contact with the lower portion of the wall of the relatively large bore 24. It is therefore a mat ter of impossibility to effect a leakage of cpl-rent from the top of the electrode member 28 over the outside surface of the exposed portion of the insulator thereby obviating all possibility of leakage from the top of the insulator t0 the metal shell of the plug which is always possible and oftentimes present in spark plugs of usual construction. It will thus be seen from the accompanying drawing taken in connection with this specification that provision has been made to protect the plug against short circuiting in any one of the three previously mentioned ways which are prevalent in spark plugs of usual construction.

Referring again to the slotted or cut electrode arranged to exert a capillary attrac tion for liquids bridging or tending to bridge the spark gap it may be said that this slotted or cut construction of the electrode presents advantages over a tubular electrode, for the reason that this present construction presents advantages from the standpoint of manufacture over the tubular construction of the electrode and further presents the very material advantage that in the tubular construction of the electrode there is always present the possibility of an infinitesimal quantity of air becoming trapped in the tubular electrode to prevent the capillary action of the same. VVith the slotted or cut construction of the electrode,

one of said electrodes being provided at the spark gap with a capillary slot entering the electrode from the side thereof to attract by capillarity a bridge of liquid across the spark gap, said capillary slot being p0- sitioned in relation to the spark gap to drain excess oil from the said slot by gravity.

8. A spark plug comprising a plurality of electrodes separated to form a spark gap, and a capillary opmling at the spark gap in and transversely of one electrode to provide an elongated aperture in the side of the electrode to attract liquid at the spark gap to prevent the bridging: of the spark gap, said capillary opening being positioned in relation to the spark gap to drain excess oil from said capillary opening, by gravity.

In testimony whereof, I aflix my signature, in presence of two witnesses.

(HA RLES HUGH DUFF Y.

\Vitnesses F REDERIUK V. PLUGGE, C. M. Fonnnsr. 

